Thomas F. Edgar
Department of Chemical Engineering
University of Texas
Austin, TX 78712

Batch Processing – Definition,
Advantages, Disadvantages
• A sequence of one more steps (recipe) usually carried out in more than one vessel and in a defined order, yielding a finished product
• Production amounts are usually smaller than for continuous processing
• Requires reduced inventories and shorter response times
• Final product quality must be satisfied with each batch (no blending)
• More emphasis on production scheduling in batch processing

Other Advantages
• Batch time can be adjusted to meet quality specs
• Repetition is conducive to continuous improvement in product
• Slow dynamics permit real-time calculations
• Greater agility

Batch Processing Used in
Manufacturing
• Electronic materials
• Specialty chemicals
• Metals
• Ceramics
• Polymers
• Food and agricultural materials
• Biochemicals
• Multiphase materials/blends
• Coatings
• Composites

Representative processing steps in a semiconductor wafer fab
(Deposition, Patterning, Etching, Doping, etc)

Unit operations in microelectronics manufacturing are characterized by:
1. Physical/chemical complexity
2. Inability to measure directly many process variables
3. High sensitivity to process changes
4. Multiple inputs/multiple outputs

CD Variation Effects in Pattern Transfer
Wafer
Flatness
Reflectivity
Topography
Reticle
CD
Defects
Edge Roughness
Proximity Effects
Stepper
Aberrations
Lens Heating
Focus
Leveling
Dose
Etch
Power
Pressure
Flow rates
Refractive Index
Thickness
Uniformity
Viscosity
Contrast
Resist PEB
Temperature
Uniformity
Time
Delay
Time
Temperature
Dispense Pattern
Rinse
Develop
Amines
Humidity
Pressure
Environment

Why Control Critical Dimension (CD)?
• Small changes in CD distribution = Large $ values lost
Higher speed
210
3 σ = 36nm
3 σ = 12nm
230 250
Gate CD (nm)
270
290

Control Hierarchy in Batch
Processing
1. Sequential control to step the process through a recipe
2. Logic control to deal with device interlocks
3. Within-the-batch control to make set point changes and reject disturbances
4. Run-to-run control to meet final quality constraints
5. Batch production control to maximize utilization of equipment and minimize cycle time

Figure 22.19 Batch control system – a more detailed view

• Time-varying process characteristics (no steady state)
• Nonlinear behavior
• Model inaccuracies
• On-line sensors often not available
• Constrained operation
• Unmeasured disturbances
• Irreversible behavior

• Keeps batch process product on target by using feedback to manipulate batch recipe for consecutive batches
• Required due to a lack of in situ, real-time measurements of product quality of interest
• Extremely useful where initial conditions or tool states are variable and unmeasurable
• Supervisory controller determines optimal setpoints for real-time control loops (typically
PID)

STI
Application: Resist etch process
SiON
Linewidth
Trimmed
Resist
Poly Silicon
Gate Oxide
Silicon Substrate
STI
• The incoming pattern is masked with linewidths greater than required.
• An additional step is added to the etch process which etches the resist pattern.
• The resist etch step trims the lines to the proper resist linewidth.
• The rest of the etch transfers the resulting mask pattern into the polysilicon, creating the poly gate structures.

30
40
pk
Prior to APC Implementation
With Automated Run-to-Run Control
20
10
0
-1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1
0 0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Normalized Deviation From Target
Metric
Mean Deviation From Target
Standard Deviation
Cpk
Uncontrolled
-0.201
0.254
1.05
Controlled
0.045
0.188
1.7
% Change
-77%
-26%
+62%

Figure 22.17 Multiproduct batch plant

Characteristics of batch scheduling and planning problems (Pekny and Reklaitis)
DETERMINE
What
Product amounts: lot sizes, batch
Sizes
When
Timing of specific operations, run lengths
Where
Sites, units, equipment items
How
Resource types and amounts
GIVEN
Product requirements
Horizon, demands, starting and
Ending inventories
Operational steps
Precedence order
Resource utilization
Production facilities
Types, capacities
Resource limitations
Types, amounts, rates

A
Multi-Product Processing Overview
B B A A B
Fab Tool
Process 1
A A A A
A B B A A B
Fab Tool
Process 1
Process 2
Fab Tool
Process 1
Process 2

2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
A B
4
3.5
3
2.5
2
1.5
1
0.5
0
Process
Correct Metrology
Ordering
A B C D E
4
3. 5
3
2. 5
2
1. 5
1
0. 5
0
Incorrect Metrology
Ordering
E D C B A
C D E
4
3.5
3
2.5
2
1.5
1
0.5
0
C D A E B
Incorrect Metrology
Ordering

Integration Across Standard
ChE Courses
• discrete logic in process operations
• design for safe operation
• measurement strategies (e.g., end point)
• batch vs. semibatch (bioreactors)
• use of fundamental (nonlinear) models
• numerical methods, statistics
• population balances
• case studies